I would say there’s the obvious industry sexism that limits it, but I do question if there’s a significant market for it? Werewolves are generally characterized as big, strong, hairy, violent, and bestial, and those tend to be characteristics a lot of women either don’t or don’t want to identify with. While there’s elements of werewolf mythos that some women might identify with, the common understanding of them as an archetype of everything that the social construction of femininity tells women they should be suppressing in themselves. While there’s certainly women out there that reject the common social construction and even actively defy it, I would suggest that that’s a rather niche market. That doesn’t excuse not publishing material for that market, lots of works do quite well playing to the niche, but I wonder if books like that would have any chance of making it into mainstream consciousness… at least without a fandom that becomes known for being a bit… rabid (I’m sorry, I had to).